4TB / 4000GB - SAS / Serial Attached SCSI Hard Drives are almost exclusively for usage in servers that use hot swappable (hot-swap) drives with a SAS hot pluggable backplane. You use a hard drive tray or caddy or sled, and simply slide and clip the drive into the front of your server. SAS hard drives can also be used in an internal, non hot-swap application. In this case they are connected by a cable to a connector on the SAS controller.
Example models are: WD4000FYYZ .
Hot-swap SAS / Serial Attached SCSI hard drives are commonly used in Dell PowerEdge 840, 1900, 1950, 1950 III, 2900, 2900 III, 2950, 2950 III, 2970, 6900, 6950, R300, R900, R905, T300, T605 Servers and PowerVault MD1000, MD3000, NF100, NF500, NF600 Storage Arrays; Compaq Proliant® systems such as DL140 G2 , DL140 G3 , DL145 G2 , DL145 G3 , DL160 G5 , DL180 G5 , DL185 G5, DL320 G3 , DL320 G4 , DL320 G5 , DL320 G5p , DL360 G4p , ML110 G3 , ML150 G3 , ML310 G2 , ML310 G3 , ML310 G4 , ML310 G5 , ML350 G4p , ML350 G5; and Ibm xSeries such as 3250, 306m, 3400, 3455, 3500, 3550, 3600, 3650, 3655, 3700, 3755, 3800, 3850.